The invention relates to an automatic focussing apparatus, and more particularly, to an automatic focussing apparatus comprising a combination of a camera which is capable of detecting a focus condition on an imaging surface to provide lens motion information which is used to drive a taking lens toward an in-focus position, and a lens barrel which is responsive to lens motion information from the camera to drive the taking lens by means of a motor.
In a conventional automatic focussing apparatus including a combination of a focussing camera and a lens barrel as described above, switches are provided on the camera and on the lens barrel, respectively, so that either switch may be turned on to activate an automatic focussing mechanism (Japanese Laid-Open Patent Application No. 49,927/1982). In this apparatus, a battery is internally housed within the camera to feed an in-focus detector circuit provided on the camera side while the lens barrel internally houses another battery which feeds a motor drive circuit for the lens barrel. This causes an inconvenience in that the automatic focussing apparatus may fail to operate or may operate in an unstable manner if the battery within the camera has been dissipated to a degree that the in-focus detector circuit is not properly fed. In particular, because of the space limitation, the battery housed within the camera is generally of a reduced capacity, and hence is exhausted rapidly. Accordingly, there is a high likelihood that the focussing mechanism may fail to operate even though the battery housed within the lens barrel has sufficient power capacity left to activate the motor drive circuit.
In an automatic focussing apparatus of the kind described, it is necessary to determine whether a deviation in the focus position represents a front or a rear focus, in order to move the taking lens in accordance with a deviation detected on the imaging surface. Thus, both the magnitude and the direction of the deviation must be transmitted from the camera to the lens barrel. This requires the provision of a pair of signal paths in order to transmit information relating to the magnitude of the deviation separately from information representing the direction of the deviation or to transmit the magnitude of the deviation on separate paths corresponding to each direction of deviation. However, it will be appreciated that a reduction in the number of signal paths between the camera and the lens barrel and hence of electrical contacts is highly desirable to achieve a simplified construction and increased reliability.